1. Field of the Invention
The present invention relates generally to an apparatus for controlling the opening and closing of a channel for a liquid and, more particularly, to an apparatus for controlling the opening and closing of a channel for a liquid such as a solution which contains a vital substance, the apparatus being arranged to close the channel by solidifying the liquid itself in the channel and to open the channel by melting the solidified liquid. The invention also relates to a method of controlling the opening and closing of such a liquid channel.
2. Description of the Related Art
In a conventional type of system for effecting automatic analysis or separation of a sample of a vital substance such as blood, protein or the like, it is customary that a solenoid valve is employed to control the opening and closing of a channel for a liquid such as a sample solution, as disclosed in, for example, Japanese Patent Publication No. 5699/1988. This is because, as is well known, solenoid valves can be easily incorporated into an automated system since they are capable of electrically controlling the opening and closing of a channel for a liquid.
However, if such a solenoid valve is applied to control of the opening and closing of a channel for a liquid such as a sample solution containing a vital substance, the following problems arise.
(1) Since the internal liquid channel of the solenoid valve includes bends, abrupt increases and decreases in diameter and uneven portions in structural terms, samples are easily fixed to the inner surface of the liquid channel.
(2) Since a valve disc is forced against a valve seat, vital samples are easily impaired and, in addition, vibration or noise occurs.
In such a system, it is customary that, after the completion of separation or analysis of a first sample, if a second sample is to be handled, the channel is cleansed to prevent mixture or contamination of the sample. However, as described in paragraph (1), since the solenoid valve has a complicated internal structure, it is difficult to promptly remove all residual sample fixed to the inner surface and a long time are therefore required for cleansing. Moreover, as described in paragraph (2), in typical applications which require this kind of system, it is necessary that occurrence of vibration or noise be avoided as far as is possible.